Touch panel

ABSTRACT

To provide a thin touch panel, a touch panel with high visibility, a lightweight touch panel, or a touch panel with low power consumption. A pair of conductive layers included in a capacitive touch sensor have a mesh shape including a plurality of openings. Furthermore, a material blocking visible light is provided to overlap with a region between two display elements in a plan view; thus, a light-blocking layer can be obtained. Furthermore, the pair of conductive layers included in the touch sensor are provided between a pair of substrates included in the touch panel, and a conductive layer capable of supplying a constant potential is provided between a circuit which drives a display element and the pair of conductive layers.

This application is a continuation of U.S. application Ser. No.15/807,218, filed on Nov. 8, 2017 is a continuation of U.S. applicationSer. No. 15/070,241, filed on Mar. 15, 2016 (now U.S. Pat. No. 9,817,536issued Nov. 14, 2017) which are all incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to an input device. Oneembodiment of the present invention relates to a display device. Oneembodiment of the present invention relates to an input/output device.One embodiment of the present invention relates to a touch panel.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention disclosed in this specification include asemiconductor device, a display device, a light-emitting device, a powerstorage device, a memory device, an electronic device, a lightingdevice, an input device, an input/output device, a driving methodthereof, and a manufacturing method thereof.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A semiconductor element such as a transistor, asemiconductor circuit, an arithmetic device, and a memory device areeach an embodiment of a semiconductor device. An imaging device, adisplay device, a liquid crystal display device, a light-emittingdevice, an input device, an input/output device, an electro-opticaldevice, a power generation device (including a thin film solar cell, anorganic thin film solar cell, and the like), and an electronic devicemay each include a semiconductor device.

2. Description of the Related Art

In recent years, a display device provided with a touch sensor as aposition-input device has been in practical use. A display deviceprovided with a touch sensor is called a touch panel, a touch screen, orthe like (hereinafter also referred to simply as a touch panel). Forexample, a smartphone and a tablet terminal are examples of a portableinformation terminal provided with a touch panel.

As one of display devices, there is a liquid crystal display deviceprovided with a liquid crystal element. For example, an active matrixliquid crystal display device, in which pixel electrodes are arranged ina matrix and transistors are used as switching elements connected torespective pixel electrodes, has attracted attention.

For example, an active matrix liquid crystal display device includingtransistors, in which metal oxide is used for a channel formationregion, as switching elements connected to respective pixel electrodesis already known (Patent Documents 1 and 2).

It is known that an active matrix liquid crystal display device isclassified into two major types: transmissive type and reflective type.

In a transmissive liquid crystal display device, a backlight such as acold cathode fluorescent lamp is used, and a state in which light fromthe backlight is transmitted through liquid crystal and output to theoutside of the liquid crystal display device or a state in which lightis not output is selected using optical modulation action of liquidcrystal, whereby bright and dark images are displayed. Furthermore,those displays are combined to display an image.

In a reflective liquid crystal display device, a state in which externallight, in other words, incident light is reflected at a pixel electrodeand output to the outside of the device or a state in which incidentlight is not output to the outside of the device is selected usingoptical modulation action of liquid crystal, whereby bright and darkimages are displayed. Furthermore, those displays are combined todisplay an image. Compared to the transmissive liquid crystal displaydevice, the reflective liquid crystal display device has the advantageof low power consumption since the backlight is not used.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2007-123861-   [Patent Document 2] Japanese Published Patent Application No.    2007-096055

SUMMARY OF THE INVENTION

What is desirable is a touch panel in which a display panel is providedwith a function of inputting data with a finger, a stylus, or the liketouching a screen as a user interface.

Furthermore, it is demanded that an electronic appliance using a touchpanel is reduced in thickness and weight. Therefore, a touch panelitself is required to be reduced in thickness and weight.

For example, in a touch panel, a touch sensor can be provided on theviewer side (the display surface side) of a display panel.

In a touch panel where a capacitive touch sensor is provided so as tooverlap with the display surface side of a display panel, when thedistance between a pixel or a wiring of the display panel and anelectrode or a wiring of the touch sensor is reduced, the touch sensoris likely to be influenced by noise caused when the display panel isdriven by the touch sensor, which results in a reduction of thedetection sensitivity of the touch panel in some cases.

One object of one embodiment of the present invention is to provide athin touch panel. Another object is to provide a touch panel with highvisibility. Another object is to provide a lightweight touch panel.Another object is to provide a touch panel with low power consumption.

Another object is to provide a novel input device. Another object is toprovide a novel input/output device.

One embodiment of the present invention is a touch panel including afirst substrate, a first conductive layer, a second conductive layer, athird conductive layer, a fourth conductive layer, and a liquid crystallayer. The third conductive layer is over the first substrate. Thefourth conductive layer is apart from the third conductive layer on thesame plane. The liquid crystal layer is positioned above the thirdconductive layer. The second conductive layer is positioned above theliquid crystal layer. The first conductive layer is positioned above thesecond conductive layer. The first conductive layer has a function ofblocking visible light and has a mesh shape including a plurality ofopenings. The second conductive layer has a function of transmittingvisible light and includes a portion overlapping with the firstconductive layer, a portion overlapping with the third conductive layer,and a portion overlapping with the fourth conductive layer. The thirdconductive layer and the fourth conductive layer each have a function ofreflecting visible light. The third conductive layer includes a portionoverlapping with one of the plurality of openings. The fourth conductivelayer includes a portion overlapping with another one of the pluralityof openings. Part of the first conductive layer is between the thirdconductive layer and the fourth conductive layer in a plan view.

In the above, it is preferable that the second conductive layer functionas a common electrode and the third conductive layer and the fourthconductive layer each function as a pixel electrode.

Another embodiment of the present invention is a touch panel including afirst substrate, a first conductive layer, a second conductive layer, athird conductive layer, a fourth conductive layer, a fifth conductivelayer, and a liquid crystal layer. The fifth conductive layer is overthe first substrate. The third conductive layer is positioned above thefifth conductive layer. The fourth conductive layer is apart from thethird conductive layer on the same plane. The liquid crystal layer ispositioned above the third conductive layer. The second conductive layeris positioned above the liquid crystal layer. The first conductive layeris positioned above the second conductive layer. The first conductivelayer has a function of blocking visible light and has a mesh shapeincluding a plurality of openings. The second conductive layer has afunction of transmitting visible light and includes a portionoverlapping with the first conductive layer, a portion overlapping withthe third conductive layer, and a portion overlapping with the fourthconductive layer. The third conductive layer and the fourth conductivelayer each have a function of reflecting visible light. The thirdconductive layer includes a portion overlapping with one of theplurality of openings. The third conductive layer and the fourthconductive layer, or the fifth conductive layer has a function ofreflecting visible light. Part of the first conductive layer is betweenthe third conductive layer and the fourth conductive layer in a planview. The third conductive layer has a comb-like shape. The one of theplurality of openings, the third conductive layer, and the fifthconductive layer overlap with one another in a region. The one of theplurality of openings and the fifth conductive layer overlap with eachother and do not overlap with the third conductive layer in a region.

Another embodiment of the present invention is a touch panel including afirst substrate, a first conductive layer, a second conductive layer, athird conductive layer, a fourth conductive layer, a fifth conductivelayer, and a liquid crystal layer. The fifth conductive layer ispositioned over the first substrate. The third conductive layer ispositioned between the fifth conductive layer and the first substrate.The fourth conductive layer is apart from the third conductive layer onthe same plane. The liquid crystal layer is positioned above the fifthconductive layer. The second conductive layer is positioned above theliquid crystal layer. The first conductive layer is positioned above thesecond conductive layer. The first conductive layer has a function ofblocking visible light and has a mesh shape including a plurality ofopenings. The second conductive layer has a function of transmittingvisible light and includes a portion overlapping with the firstconductive layer, a portion overlapping with the third conductive layer,and a portion overlapping with the fourth conductive layer. The thirdconductive layer includes a portion overlapping with one of theplurality of openings. The fourth conductive layer includes a portionoverlapping with another one of the plurality of openings. The thirdconductive layer and the fourth conductive layer, or the fifthconductive layer has a function of reflecting visible light. Part of thefirst conductive layer is between the third conductive layer and thefourth conductive layer in a plan view. The fifth conductive layer has acomb-like shape. The one of the plurality of openings, the thirdconductive layer, and the fifth conductive layer overlap with oneanother in a region. The one of the plurality of openings and the fifthconductive layer overlap with each other and do not overlap with thethird conductive layer in a region.

In the above, it is preferable that one of the third conductive layerand the fifth conductive layer function as a pixel electrode, and theother function as a common electrode. Alternatively, it is preferablethat the third conductive layer and the fourth conductive layer eachfunction as a pixel electrode and the fifth conductive layer function asa common electrode.

The second conductive layer is preferably electrically connected to aterminal supplied with a constant potential.

In the above, a second substrate is preferably above the firstconductive layer. At this time, the first conductive layer and thesecond conductive layer are preferably formed over the second substrate:

In the above, it is preferable that a first coloring layer and a secondcoloring layer be positioned above the third conductive layer, the firstcoloring layer include a region overlapping with the one of theplurality of openings, and the second coloring layer include a regionoverlapping with the another one of the plurality of openings.

In the above, the first conductive layer preferably includes a portionoverlapping with at least one of the first coloring layer and the secondcoloring layer.

In the above, it is preferable that a spacer be provided above the thirdconductive layer and below the second conductive layer and include aportion overlapping with the first conductive layer.

In the above, it is preferable that a transistor be between the liquidcrystal layer and the first substrate, one of a source and a drain ofthe transistor be electrically connected to the third conductive layer,and the transistor include a semiconductor layer containing an oxidesemiconductor.

In this case, the transistor preferably includes a first gate electrodeand a second gate electrode. It is preferable that the first gateelectrode be positioned below the semiconductor layer, the second gateelectrode be positioned above the semiconductor layer, and the secondgate electrode, the semiconductor layer, and the third conductive layeroverlap with one another in a region. Moreover, in this case, the secondgate electrode and the semiconductor layer preferably contain the samemetal element.

According to one embodiment of the present invention, a thin touch panelcan be provided. Alternatively, a touch panel with high visibility canbe provided. Alternatively, a lightweight touch panel can be provided.Alternatively, a touch panel with low power consumption can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a structure example of a touch panel module of anembodiment.

FIG. 2 shows a structure example of a touch panel module of anembodiment.

FIG. 3 shows a structure example of a touch panel module of anembodiment.

FIG. 4 shows a structure example of a touch panel module of anembodiment.

FIG. 5 shows a structure example of a touch panel module of anembodiment.

FIG. 6 shows a structure example of a touch panel module of anembodiment.

FIG. 7 shows a structure example of a touch panel module of anembodiment.

FIG. 8 shows a structure example of a touch panel module of anembodiment.

FIGS. 9A to 9C show structure examples of a touch sensor of anembodiment.

FIGS. 10A to 10C show structure examples of a touch sensor of anembodiment.

FIGS. 11A and 11B show structure examples of a touch sensor of anembodiment.

FIGS. 12A to 12G show structure examples of a touch panel of anembodiment.

FIGS. 13A and 13B are a block diagram and a timing chart of a touchsensor of an embodiment.

FIG. 14 is a circuit diagram of a touch sensor of an embodiment.

FIGS. 15A and 15B each illustrate a pixel provided with a touch sensorof an embodiment.

FIGS. 16A and 16B illustrate operation of a touch sensor and a pixel ofan embodiment.

FIG. 17 illustrates a display module of an embodiment.

FIGS. 18A to 18H each illustrate an electronic device of an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the description below, andit is easily understood by those skilled in the art that various changesand modifications can be made without departing from the spirit andscope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the content of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Furthermore, the same hatching pattern isapplied to portions having similar functions, and the portions are notespecially denoted by reference numerals in some cases.

Note that in each drawing described in this specification, the size, thelayer thickness, or the region of each component is exaggerated forclarity in some cases. Therefore, embodiments of the present inventionare not limited to such a scale.

Note that in this specification and the like, ordinal numbers such as“first”, “second”, and the like are used in order to avoid confusionamong components and do not limit the number.

Note that the terms “film” and “layer” can be interchanged with eachother in some cases. For example, in some cases, the term “conductivefilm” can be used instead of the term “conductive layer,” and the term“insulating layer” can be used instead of the term “insulating film.”

Embodiment 1

In this embodiment, a structure example of an input device (a touchsensor) of one embodiment of the present invention, and a structureexample of an input/output device (a touch panel) including the inputdevice of one embodiment of the present invention and a display device(a display panel) are described with reference to drawings.

In the description below, a capacitive touch sensor is used as the touchsensor of one embodiment of the present invention.

Note that in this specification and the like, a touch panel has afunction of displaying or outputting an image or the like on or to adisplay surface and a function as a touch sensor capable of detectingcontact or proximity of an object such as a finger or a stylus on or tothe display surface. Therefore, the touch panel is an embodiment of aninput/output device.

In this specification and the like, a structure in which a connectorsuch as a flexible printed circuit (FPC) or a tape carrier package (TCP)is attached to a substrate of a touch panel, or a structure in which anintegrated circuit (IC) is directly mounted on a substrate by a chip onglass (COG) method is referred to as a touch panel module or simplyreferred to as a touch panel in some cases.

A capacitive touch sensor that can be used for one embodiment of thepresent invention includes a pair of conductive layers. A capacitor isformed in the pair of conductive layers. The capacitance of the pair ofconductive layers changes when an object touches or gets close to thepair of conductive layers. Utilizing this effect, detection can beconducted.

Examples of the capacitive touch sensor are a surface capacitive touchsensor and a projected capacitive touch sensor. Examples of a projectedcapacitive touch sensor are a self-capacitive touch sensor and a mutualcapacitive touch sensor. The use of a mutual capacitive touch sensor ispreferable because multiple points can be detected simultaneously.

It is preferable that a pair of conductive layers included in the touchsensor each have an opening. It is more preferable that the pair ofconductive layers have a mesh shape having a plurality of openings. Itis preferable that the opening and a display element overlap with eachother. Such a structure enables extraction of light emitted from thedisplay element to the outside through the opening, and therefore, thepair of conductive layers included in the touch sensor do notnecessarily have a light-transmitting property. That is, a material suchas metal or alloy that has lower resistance than a light-transmittingconductive material can be used as a material for the pair of conductivelayers included in the touch sensor. This reduces the influence ofdetection signal delay or the like and increases the detectionsensitivity of the touch panel. Furthermore, such a structure can beapplied to large-sized display devices such as televisions as well asportable devices.

Furthermore, it is preferable that the pair of conductive layersincluded in the touch sensor be provided to overlap with a regionbetween two display elements in a plan view. In this case, it is morepreferable that a material blocking visible light be used for the pairof conductive layers. Such a structure allows the pair of conductivelayers to function as a light-blocking layer for preventing colormixture between adjacent pixels. Thus, it is not necessary to provide ablack matrix or the like as a light-blocking layer and the manufacturingprocess can be simplified, which leads to high yield, low manufacturingcost, and the like. Moreover, by applying such a touch sensor, a touchpanel having high visibility can be obtained.

Furthermore, the pair of conductive layers included in the touch sensorare provided in a region other than an optical path of light from thedisplay element; thus, moire is not generated in principle. Here, moiremeans interference fringes generated in the case where two or moreregular patterns overlap with each other. As a result, a touch panelhaving extremely high display quality can be obtained.

As a display element in a touch panel of one embodiment of the presentinvention, a variety of display elements, for example, a liquid crystalelement, an optical element utilizing micro electro mechanical systems(MEMS), a light-emitting element such as an organic electroluminescence(EL) element or a light-emitting diode (LED), and an electrophoreticelement can be used.

Here, a reflective liquid crystal display device including a liquidcrystal element as a display element is preferably used for the touchpanel. A reflective liquid crystal display device consumes much lowerpower than a transmissive liquid crystal display device.

Moreover, it is preferable that the pair of conductive layers includedin the touch sensor be provided between a pair of substrates included inthe touch panel. In particular, it is preferable that the conductivelayer included in the touch sensor have a plurality of openings. Such aconductive layer can have a smaller surface area. Therefore, electricalnoise in driving of the display element is hardly transmitted to theconductive layer as compared with the case where a light-transmittingconductive film without openings is used as the conductive layerincluded in the touch sensor, for example. In other words, even whenboth a display element and a conductive film included in the touchsensor are provided between the pair of substrates, high detectionsensitivity can be achieved. As a result, a thin touch panel having highdetection sensitivity can be provided.

Furthermore, it is more preferable that a conductive layer capable ofsupplying a constant potential be provided between a circuit for drivinga display element and the pair of conductive layers included in thetouch sensor. Such a conductive layer can function as a shield layer.Specifically, the conductive layer can prevent transmission of noisefrom the circuit for driving the display element to the touch sensor.The conductive layer can also prevent transmission of noise in drivingof the touch sensor to the display element, the circuit for driving thedisplay element, a wiring included in the circuit, or the like.Therefore, the display element and the touch sensor can be driven at thesame time or can be driven not in synchronization without takingmeasures, for example, without preventing influence of noise by drivingthe display element and the touch sensor at different timings. As aresult, a smooth moving image can be displayed by, for example,increasing the drive frequency (also referred to as frame rate) of thedisplay element. Furthermore, the sensing accuracy can be increased by,for example, increasing the drive frequency of the touch sensor.Moreover, the drive frequency of the display element and the drivefrequency of the touch sensor each can be freely set. For example, byproviding a period during which one or both of the drive frequencies arelow depending on conditions, power consumption can be reduced.

With the use of a reflective liquid crystal display device for the touchpanel, a structure without a backlight can be employed. Thus, byproviding a conductive film included in a touch sensor and a reflectiveliquid crystal element between a pair of substrates, a touch panel whosethickness is synergistically reduced can be provided.

A more specific structure example of one embodiment of the presentinvention is described below with reference to drawings.

[Structure Example]

FIG. 1A is a schematic perspective view of a touch panel module 10 ofone embodiment of the present invention. FIG. 1B is a schematicperspective view of the touch panel module 10 in which a pair ofsubstrates are separated. In the touch panel module 10, a substrate 31and a substrate 21 are attached to each other. The touch sensor 22 isprovided on the substrate 21 side.

The substrate 21 is provided with an FPC 41. Furthermore, the touchsensor 22 is provided on a surface on the display panel 30 side of thesubstrate 21. The touch sensor 22 includes a conductive layer 23, aconductive layer 24, a conductive layer 25, and the like. Furthermore,the touch sensor 22 includes a wiring 29 which electrically connectsthese conductive layers to the FPC 41. The FPC 41 has a function ofsupplying a signal from the outside to the touch sensor 22. Furthermore,the FPC 41 has a function of outputting a signal from the touch sensor22 to the outside. Note that the substrate without the FPC 41 is simplyreferred to as a touch panel.

Note that the substrate 21 over which the touch sensor 22 is formed alsocan be used alone as a touch sensor substrate or a touch sensor module.For example, such a substrate can be attached to the display surfaceside of the display panel to form a touch panel.

The touch sensor 22 includes a plurality of conductive layers 23, aplurality of conductive layers 24, and a plurality of conductive layers25. Each of the conductive layers 23 has a shape extending in onedirection. The plurality of conductive layers 23 are arranged in adirection crossing the extending direction. Each of the conductivelayers 24 is positioned between two adjacent conductive layers 23. Eachof the conductive layers 25 electrically connects two conductive layers24 adjacent in the direction crossing the extending direction of theconductive layers 23. That is, the plurality of conductive layers 24arranged in the direction crossing the extending direction of theconductive layers 23 are electrically connected to each other with theplurality of conductive layers 25.

Here, there is a region where the conductive layer 23 and the conductivelayer 25 overlap with each other. An insulating layer is providedbetween the conductive layer 23 and the conductive layer 25.

A capacitor is formed in the conductive layers 23 and 24 adjacent toeach other. For example, in the case of employing a projected capacitivedriving method, one of the conductive layers 23 and 24 can be used as atransmission-side electrode, and the other thereof can be used as areception-side electrode.

Note that here, the plurality of conductive layers 24 are electricallyconnected to each other with the conductive layer 25. Alternatively, itis possible to employ a structure in which the conductive layer 24 has ashape extending in one direction like the conductive layer 23, aninsulating layer is provided between the conductive layer 23 and theconductive layer 24, and the conductive layer 25 is not provided. Inthis case, the conductive layer 23 and the conductive layer 24 partlyoverlap with each other.

Note that, for example, a low-resistance material is preferably used asa material of conductive films such as the conductive layer 23, theconductive layer 24, and the conductive layer 25, i.e., a wiring and anelectrode in the touch panel. As an example, metal such as silver,copper, or aluminum may be used. Alternatively, a metal nanowireincluding a number of conductors with an extremely small width (forexample, a diameter of several nanometers) may be used. Examples of sucha metal nanowire include an Ag nanowire, a Cu nanowire, and an Alnanowire. In the case of using an Ag nanowire, light transmittance of89% or more and a sheet resistance of 40 ohm/square or more and 100ohm/square or less can be achieved. Note that because such a metalnanowire provides high transmittance, the metal nanowire may be used foran electrode of the display element, e.g., a pixel electrode or a commonelectrode.

A display portion 32 is provided over the substrate 31. The displayportion 32 includes a plurality of pixels 33 arranged in a matrix. Eachpixel 33 preferably includes a plurality of sub-pixel circuits. Eachsub-pixel circuit is electrically connected to a display element. Acircuit 34 electrically connected to the pixel 33 in the display portion32 is preferably provided over the substrate 31. For example, a circuitfunctioning as a gate driver circuit can be used as the circuit 34. AnFPC 42 has a function of supplying a signal from the outside to at leastone of the display portion 32 and the circuit 34. An IC functioning as asource driver circuit is preferably mounted on the substrate 31 or theFPC 42. The IC can be mounted on the substrate 31 by a COG method.Alternatively, the FPC 42, a TAB, a TCP, or the like on which an IC ismounted can be attached to the substrate 31.

The touch panel module of one embodiment of the present invention canoutput positional information based on the change in capacitance by thetouch sensor 22 at the time of a touch motion. Furthermore, the displayportion 32 can display an image.

[Cross-Sectional Structure Example]

A cross-sectional structure example of the touch panel module 10 isdescribed below with reference to drawings. The touch panel module 10described below as an example is a module in which a reflective liquidcrystal element is used as a display element.

[Cross-Sectional Structure Example 1]

FIG. 2 is a schematic cross-sectional view of the touch panel module 10.FIG. 2 illustrates cross sections of a region including the FPC 42, aregion including the circuit 34, a region including the display portion32, a region including the FPC 41, and the like in FIG. 1A.

The substrate 21 and the substrate 31 are attached to each other with anadhesive layer 141. A region surrounded by the substrate 21, thesubstrate 31, and the adhesive layer 141 is filled with a liquid crystal112. A polarizing plate 130 is provided on an outer surface of thesubstrate 21.

The touch sensor 22 including the conductive layer 23 and the conductivelayer 24, a connection portion 101, a wiring 29, a display element 60, atransistor 201, a transistor 202, a capacitor 203, a connection portion204, a wiring 35, and the like are provided between the substrate 31 andthe substrate 21.

Insulating layers such as an insulating layer 211, an insulating layer212, an insulating layer 213, and an insulating layer 214 are providedover the substrate 31. Part of the insulating layer 211 functions as agate insulating layer of each transistor, and another portion thereoffunctions as a dielectric of the capacitor 203. The insulating layer212, the insulating layer 213, and the insulating layer 214 are providedto cover each transistor, the capacitor 203, and the like. Theinsulating layer 214 functions as a planarization layer. Note that anexample where the three insulating layers, the insulating layers 212,213, and 214, are provided to cover the transistors and the like isdescribed here; however, the present invention is not limited to thisexample, and four or more insulating layers, a single insulating layer,or two insulating layers may be provided. The insulating layer 214functioning as a planarization layer is not necessarily provided whennot needed.

A conductive layer 221, a conductive layer 222, a conductive layer 223,a semiconductor layer 231, a conductive layer 111, and the like areprovided over the substrate 31. Here, a plurality of layers obtained byprocessing the same conductive film are denoted by the same referencenumeral in some cases.

The conductive layer 221 can be used for a gate electrode of eachtransistor, one electrode of the capacitor 203, a wiring, or the like.The conductive layer 222 can be used for a source electrode or a drainelectrode of each transistor, one electrode of a capacitor, a wiring, orthe like. The conductive layer 223 can be used for another gateelectrode of each transistor, a wiring, or the like. The semiconductorlayer 231 can be used for a semiconductor layer of a transistor or thelike.

FIG. 2 illustrates an example of cross sections of a sub-pixel 33R andparts of a sub-pixel 33G and a sub-pixel 33B which are adjacent to thesub-pixel 33R in the display portion 32. For example, the sub-pixel 33Ris a sub-pixel exhibiting a red color, the sub-pixel 33G is a sub-pixelexhibiting a green color, and the sub-pixel 33B is a sub-pixelexhibiting a blue color; thus, full-color display can be achieved. Thesub-pixel 33R includes, for example, the transistor 202, the capacitor203, the display element 60, and a coloring layer 131R. Here, thesub-pixel circuit includes the transistor 202, the capacitor 203, awiring, and the like.

FIG. 2 illustrates an example of the circuit 34 in which the transistor201 is provided.

In the example illustrated in FIG. 2, the transistors 201 and 202 eachhave a structure in which the semiconductor layer 231 where a channel isformed is provided between two gate electrodes (conductive layers 221and 223). Such transistors can have higher field-effect mobility andthus have higher on-state current than other transistors. Consequently,a circuit capable of high-speed operation can be obtained. Furthermore,the area occupied by a circuit portion can be reduced. The use of thetransistor having high on-state current can reduce signal delay inwirings and can reduce display unevenness even in a display panel or atouch panel in which the number of wirings is increased because ofincrease in size or resolution.

It is preferable that the conductive layer 111 be provided to overlapwith the semiconductor layer 231 of the transistor 202 as illustrated inFIG. 2 because the aperture ratio of the sub-pixels can be increased. Inthis case, the conductive layer 223 is preferably provided between theconductive layer 111 and the semiconductor layer 231. The conductivelayer 223 prevents influence of the electric field of the conductivelayer 111 on the semiconductor layer 231, and a malfunction issuppressed. In the case where the conductive layer 223 is not provided,the semiconductor layer 231 and the conductive layer 111 are preferablyprovided not to overlap with each other as illustrated in FIG. 3, forexample.

Note that the transistor included in the circuit 34 and the transistorincluded in the display portion 32 may have the same structure. Aplurality of transistors included in the circuit 34 may have the samestructure or different structures. A plurality of transistors includedin the display portion 32 may have the same structure or differentstructures.

A material through which impurities such as water or hydrogen do noteasily diffuse is preferably used for at least one of the insulatinglayers 212 and 213 which cover the transistors. That is, the insulatinglayer 212 or the insulating layer 213 can function as a barrier film.Such a structure can effectively suppress diffusion of the impuritiesinto the transistors from the outside, and a highly reliable touch panelcan be provided.

The conductive layer 111 is provided over the insulating layer 214. Theconductive layer 111 is electrically connected to one of a source and adrain of the transistor 202 through an opening formed in the insulatinglayer 214, the insulating layer 213, the insulating layer 212, and thelike. The conductive layer 111 is also electrically connected to oneelectrode of the capacitor 203.

The conductive layer 23, the conductive layer 24, the conductive layer25, the wiring 29, an insulating layer 121, an overcoat 123, a spacer124, a coloring layer 131G, the coloring layer 131R, a coloring layer131B, a conductive layer 113, and the like are provided on the substrate31 side of the substrate 21.

In FIG. 2, a cross section of an intersection of the conductive layer 23and the conductive layer 24 is illustrated. The conductive layer 23 andthe conductive layer 24 are provided on the same plane. The insulatinglayer 121 is provided between the conductive layer 25 and the conductivelayers 23 and 24. Part of the conductive layer 25 overlaps with theconductive layer 23. The two conductive layers 24 between which theconductive layer 23 is provided are electrically connected to theconductive layer 25 through openings provided in the insulating layer121.

The coloring layer 131R and the like are provided on the substrate 31side of the insulating layer 121. The overcoat 123 is provided to coverthe coloring layer 131R and the like. The conductive layer 113 isprovided on the substrate 31 side of the overcoat 123.

In FIG. 2, the display element 60 includes the conductive layer 111,part of the conductive layer 113, and the liquid crystal 112 sandwichedtherebetween.

Alignment films for controlling alignment of the liquid crystal 112 maybe provided on surfaces of the conductive layers 111 and 113, theinsulating layer 214, and the like which are in contact with the liquidcrystal 112.

In the structure of FIG. 2, the conductive layer 23 is provided not tooverlap with the display element 60. In other words, the conductivelayer 23 is provided so that the display element 60 overlaps with anopening in the conductive layer 23. In still other words, the conductivelayer 23 is provided to overlap with a region between the two conductivelayers 111 of two adjacent sub-pixels. Although an example of theconductive layer 23 is described here, it is preferable that theconductive layer 24 and the conductive layer 25 be also provided not tooverlap with the display element 60.

In the display element 60, the conductive layer 111 has a function ofreflecting visible light, and the conductive layer 113 has a function oftransmitting visible light. By having such a structure, the displayelement 60 can be a reflective liquid crystal element. Light whichenters from the polarizing plate 130 side and is polarized by thepolarizing plate 130, for example, passes through the substrate 21 andthe conductive layer 113, is reflected by the conductive layer 111,passes through the conductive layer 113 and the substrate 21 again, andthen reaches the polarizing plate 130. In this case, alignment of theliquid crystal 112 is controlled with a voltage that is applied betweenthe conductive layers 111 and 113, and thus optical modulation of lightcan be controlled. That is, the intensity of light emitted through thepolarizing plate 130 can be controlled. Light other than one in aparticular wavelength region of the incident light is absorbed by thecoloring layer 131R, and thus, reflected light, i.e., emitted light, isred light, for example. As the polarizing plate 130, a circularlypolarizing plate can be used, for example. An example of a circularlypolarizing plate is a stack including a linear polarizing plate and aquarter-wave retardation plate.

Here, as for the display element 60, a pair of electrodes are providedin the thickness direction of the touch panel module 10 and an electricfield is applied to the liquid crystal 112 in the thickness direction.The arrangement of the electrodes is not limited thereto, and a methodin which an electric field is applied in a direction perpendicular tothe thickness direction may be employed.

Liquid crystal elements using a variety of modes can be used as theliquid crystal element which can be used for the display element 60. Forexample, a liquid crystal element using a vertical alignment (VA) mode,a twisted nematic (TN) mode, an in-plane switching (IPS) mode, a fringefield switching (FFS) mode, an axially symmetric aligned micro-cell(ASM) mode, an optically compensated birefringence (OCB) mode, aferroelectric liquid crystal (FLC) mode, an antiferroelectric liquidcrystal (AFLC) mode, or the like can be used.

Furthermore, a normally black liquid crystal display device, forexample, a transmissive liquid crystal display device using a verticalalignment (VA) mode may be used as the touch panel module 10. Someexamples are given as the vertical alignment mode; for example, amulti-domain vertical alignment (MVA) mode, a patterned verticalalignment (PVA) mode, or an advanced super view (ASV) mode can be used.

The liquid crystal element controls transmission or non-transmission oflight utilizing an optical modulation action of liquid crystal. Notethat optical modulation action of liquid crystal is controlled by anelectric field applied to the liquid crystal (including a horizontalelectric field, a vertical electric field, or an oblique electricfield). As the liquid crystal used for the liquid crystal element,thermotropic liquid crystal, low-molecular liquid crystal,high-molecular liquid crystal, polymer dispersed liquid crystal (PDLC),ferroelectric liquid crystal, anti-ferroelectric liquid crystal, or thelike can be used. These liquid crystal materials exhibit a cholestericphase, a smectic phase, a cubic phase, a chiral nematic phase, anisotropic phase, or the like depending on conditions.

As the liquid crystal material, either of a positive liquid crystal anda negative liquid crystal may be used, and an appropriate liquid crystalmaterial can be used depending on the mode or design to be used.

Here, the conductive layer 113 can be used as a common electrode, andthe conductive layer 111 can be used as a pixel electrode.

In FIG. 2, the conductive layer 113 is provided to overlap with theconductive layers 23 to 25 and the like. By applying a common potential,a ground potential, or an arbitrary constant potential to the conductivelayer 113, electrical noise generated to the substrate 31 side when theconductive layers 23 to 25 are driven can be blocked. Furthermore,electrical noise generated to the substrate 21 side when the sub-pixelcircuit provided on the substrate 31 side is driven can be blocked.

The connection portion 204 is provided in a region near an end portionof the substrate 31. The connection portion 204 is electricallyconnected to the FPC 42 through a connection layer 242. FIG. 2illustrates an example of the connection portion 204 formed by stackingpart of the wiring 35 and the conductive layer 223. The connectionportion 101 is provided in a region near an end portion of the substrate21. The connection portion 101 is electrically connected to the FPC 41through a connection layer 241. In the example of the structureillustrated in FIG. 2, the connection portion 101 is formed by stackingpart of the wiring 29, a conductive layer formed by processing theconductive film used for forming the conductive layer 25, and aconductive layer formed by processing the conductive film used forforming the conductive layer 113.

In FIG. 2, a cross-sectional structure of an intersection of theconductive layer 221 functioning as a wiring and the conductive layer222 functioning as a wiring is illustrated as an example. The conductivelayer 221 can be used as one or both of a wiring functioning as a scanline and a wiring functioning as a capacitor line, and the conductivelayer 222 can be used as a wiring functioning as a signal line, forexample.

A substrate with which an object to be sensed, such as a finger or astylus, is to be in contact may be provided above the polarizing plate130. In that case, a protective layer (such as a ceramic coat) ispreferably provided over the substrate. The protective layer can beformed using an inorganic insulating material such as silicon oxide,aluminum oxide, yttrium oxide, or yttria-stabilized zirconia (YSZ).Alternatively, tempered glass may be used for the substrate. Thetempered glass which can be used here is one that has been subjected tophysical or chemical treatment by an ion exchange method, a thermaltempering method, or the like and has a surface to which compressivestress has been added.

The overcoat 123 has a function of preventing impurities such as apigment included in the coloring layer 131R or the like from diffusinginto the liquid crystal 112.

The spacer 124 is provided over the conductive layer 113 and has afunction of keeping a certain distance between the substrate 21 and thesubstrate 31. Although FIG. 2 illustrates an example where the spacer124 is not in contact with structures (e.g., the conductive layer 111and the insulating layer 214) on the substrate 31 side, the spacer 124may be in contact with them. Moreover, FIG. 2 illustrates an examplewhere the spacer 124 is provided on the substrate 21 side; however, thespacer 124 may be provided on the substrate 31 side. For example, thespacer 124 may be provided between the two conductive layers 111 of thetwo adjacent sub-pixels. Alternatively, a particulate spacer may be usedas the spacer 124. Although a material such as silica can be used forthe particulate spacer, an elastic material such as an organic resin orrubber is preferably used. In some cases, the particulate spacer may bevertically crushed.

It is preferable that the spacer 124 and the conductive layer 23 (or theconductive layer 24 or 25) be provided to overlap with each other asillustrated in FIG. 2. In such a structure, the spacer 124 is notprovided in a portion where the display element 60 is provided, in whichcase absorption, refraction, or diffusion of light due to the spacer 124does not occur, for example; thus, the light-extraction efficiency canbe improved.

In the touch panel module 10 of one embodiment of the present invention,the conductive layers 23 to 25 can function as light-blocking layers forsuppressing color mixture between adjacent sub-pixels. For that reason,a material which blocks visible light is preferably used for theconductive layers 23 to 25. Alternatively, a material reflecting visiblelight may be used. A structure in which a layer containing a materialwhich reflects visible light and a layer absorbing at least part ofvisible light in a position closer to the substrate 31 than that of theformer layer are stacked is preferable because light reaching theconductive layer 23 or the like of light reflected by the conductivelayer 111 is prevented from being reflected to the substrate 31 sideagain.

It is preferable that end portions of two adjacent coloring layersoverlap with each other to further overlap with the conductive layer 23or the like as illustrated in FIG. 4, for example. In FIG. 4, theconductive layer 23, an end portion of the coloring layer 131G, and anend portion of the coloring layer 131R overlap with one another in thevicinity of a boundary between the sub-pixel 33G and the sub-pixel 33R.The conductive layer 23, an end portion of the coloring layer 131R, andan end portion of the coloring layer 131B are provided to overlap withone another in the vicinity of a boundary between the sub-pixel 33R andthe sub-pixel 33B. Such a structure does not require additionallyproviding a layer absorbing visible light, which leads to lowermanufacturing cost. Although only one coloring layer may overlap withthe conductive layer 23 or the like, visible light can be moreeffectively absorbed when two or more coloring layers overlap with theconductive layer 23.

The above is the description of Cross-sectional Structure Example 1.

[Cross-Sectional Structure Example 2]

A cross-sectional structure example of the touch panel module 10 thatincludes a liquid crystal element having a mode different from that inCross-sectional Structure Example 1 is described below. Note thatdescriptions of the portions already described are omitted and differentportions are described below.

FIG. 5 illustrates an example where the display element 60 is a liquidcrystal element using an FFS mode. The display element 60 includes aconductive layer 151, a liquid crystal 152, and a conductive layer 153.

The conductive layer 153 is provided over the insulating layer 214. Theinsulating layer 215 is provided to cover the conductive layer 153, andthe conductive layer 151 is provided over the insulating layer 215. Theconductive layer 151 is electrically connected to one of a source and adrain of the transistor 202 through an opening provided in theinsulating layers 212 to 215.

The top surface shape of the conductive layer 151 is a comb-like shapeor has a slit. The conductive layer 153 is provided to overlap with theconductive layer 151. There is a portion where the conductive layer 151is not provided over the conductive layer 153 in a region overlappingwith the coloring layer 131R and the like.

In the structure illustrated in FIG. 5, the conductive layer 151functions as a pixel electrode, and the conductive layer 153 functionsas a common electrode. Note that the conductive layer 151 which isprovided in an upper layer and whose top surface shape is a comb-likeshape or has a slit may function as a common electrode, and theconductive layer 153 provided in a lower layer may function as a pixelelectrode. In this case, the conductive layer 153 may be electricallyconnected to one of the source and the drain of the transistor 202.

Even in the case of a horizontal electric field mode such as an FFS modeor an IPS mode, the conductive layer 113 can function as a shield layerfor suppressing the adverse effect of noise. In this case, a constantpotential which does not influence switching of the liquid crystal 152may be supplied to the conductive layer 113. For example, a groundpotential, a common potential, or an arbitrary constant potential can beused. The conductive layer 153 and the conductive layer 113 may be setat the same potential, for example.

One or both of the conductive layers 151 and 153 can be formed using amaterial that reflects visible light. When both of them are formed usinga material that reflects visible light, the aperture ratio can beincreased. The conductive layer 153 may be formed using a material thatreflects visible light and the conductive layer 151 may be formed usinga material that transmits visible light.

Alternatively, in the case of employing a horizontal electric fieldmode, a liquid crystal exhibiting a blue phase for which an alignmentfilm is unnecessary may be used. A blue phase is one of liquid crystalphases, which is generated just before a cholesteric phase changes intoan isotropic phase while temperature of cholesteric liquid crystal isincreased. Since the blue phase appears only in a narrow temperaturerange, a liquid crystal composition in which several weight percent ormore of a chiral material is mixed is used for the liquid crystal layerin order to improve the temperature range. The liquid crystalcomposition which includes liquid crystal exhibiting a blue phase and achiral material has a short response time and optical isotropy. Inaddition, the liquid crystal composition which includes liquid crystalexhibiting a blue phase and a chiral material has a small viewing angledependence. An alignment film does not need to be provided and rubbingtreatment is thus not necessary; accordingly, electrostatic dischargedamage caused by the rubbing treatment can be prevented and defects anddamage of the liquid crystal display device in the manufacturing processcan be reduced.

FIG. 6 illustrates an example where the conductive layer 223 is notprovided in the structure in FIG. 5. In the case where the conductivelayer 153 is used as a common electrode, the conductive layer 153 ispreferably provided between the semiconductor layer 231 of thetransistor 202 and the conductive layer 151 as illustrated in FIG. 6.Thus, an electric field of the conductive layer 151 can be preventedfrom affecting the semiconductor layer 231.

The above is the description of Cross-sectional Structure Example 2.

[Cross-Sectional Structure Example 3]

A cross-sectional structure example of the touch panel module 10including a touch sensor having a structure different from those inCross-sectional Structure Examples 1 and 2 is described below. Note thatdescriptions of the portions already described are omitted and differentportions are described below.

The touch panel module in FIG. 7 is different from that in FIG. 5 inthat a conductive layer 125 is provided instead of the conductive layer25 and an insulating layer 122 is provided.

The conductive layer 125 in FIG. 7 is formed using a conductive materialincluding a metal oxide.

Among the light-transmitting conductive materials which are describedlater, metal oxides can be used, for example.

Alternatively, a low-resistance oxide semiconductor is preferablyincluded. In particular, in the case where an oxide semiconductor isused for a semiconductor layer of a transistor in the touch panel module10, an oxide semiconductor whose resistivity is lower than that of theoxide semiconductor is preferably used for the conductive layer 125.

The resistivity of the conductive layer 125 can be reduced, for example,by a method for controlling the resistivity of an oxide semiconductorwhich is described later.

In this case, an insulating layer containing much hydrogen is preferablyused as the insulating layer 122 covering the conductive layer 125. Inparticular, the insulating layer 122 preferably includes an insulatingfilm containing silicon nitride.

The use of a conductive metal oxide or a low-resistance oxidesemiconductor for the conductive layer 125 suppresses oxidation of itssurface, so that the touch panel module 10 having high reliability canbe provided.

The above is the description of Cross-sectional structure example 3.

[Cross-Sectional Structure Example 4]

FIG. 8 illustrates an example of a touch panel of one embodiment of thepresent invention that includes a top-gate transistor.

A touch panel module in FIG. 8 is different from that in FIG. 5 mainlyin structures of the transistors 301 and 302. Since structures otherthan the transistor structures are almost the same as those in FIG. 5,the same portions are denoted by the same reference numerals anddetailed descriptions of common portions are omitted.

FIG. 8 illustrates an example where the display element 60 is a liquidcrystal element using an FFS mode. The display element 60 includes theconductive layer 151, the liquid crystal 152, and the conductive layer153.

The transistors 301 and 302 each include a semiconductor layer over abuffer layer 300, an insulating layer functioning as a gate insulatinglayer, a conductive layer functioning as a gate electrode andoverlapping with the semiconductor layer with the gate insulating layerprovided therebetween, an insulating layer covering the conductive layerfunctioning as the gate electrode, a conductive layer functioning as asource electrode, and a conductive layer functioning as a drainelectrode. A region of the semiconductor layer which does not overlapwith the gate electrode preferably has lower resistance than a channelformation region overlapping with the gate electrode.

In the case of using an oxide semiconductor layer, an impurity element(a rare gas, nitrogen, phosphorus, boron, hydrogen, or the like) ispreferably added to a semiconductor layer not overlapping with the gateelectrode so that the region of the semiconductor layer not overlappingwith the gate electrode has lower resistance than the channel formationregion. Helium, argon, or the like can be used as the rare gas. To addimpurities, a method using plasma, an ion implantation method, or thelike can be used. An ion implantation method is preferable becauseimpurity elements can be added using the gate electrode as a mask toreduce the resistance of part of the oxide semiconductor layer.

The capacitor 203 includes the conductive layer functioning as the gateelectrode, the conductive layer functioning as the source electrode orthe drain electrode, and an insulating layer provided therebetween as adielectric. The connection portion 204 is formed by stacking part of thewiring 35 and the conductive layer 223. The conductive layer 223 isformed by a sputtering method in an atmosphere containing an oxygen gas,and thus, oxygen or excess oxygen is added to the insulating layer 212over which the conductive layer 223 is formed. Furthermore, excessoxygen fills oxygen vacancies in the oxide semiconductor layers in thetransistors 301 and 302; thus, a highly reliable transistor can beprovided. In the case where excess oxygen is supplied to one or both ofthe insulating layer 212 and the oxide semiconductor layer, theinsulating layer 213 is preferably formed using a material capable ofsuppressing penetration of oxygen.

The buffer layer 300 is formed using an insulating material such assilicon oxide or metal oxide. As the metal oxide used for the bufferlayer 300, an oxide containing one or more of aluminum, indium, gallium,zinc, and the like is used. For the buffer layer 300, a material throughwhich impurities such as water and hydrogen are hardly diffused ispreferably used. In other words, the buffer layer 300 can function as abarrier film. Such a structure can effectively suppress diffusion of theimpurities into the transistors 301 and 302 from the outside, and thus,a highly reliable touch panel can be provided.

[Components]

The above-mentioned components are described below.

[Substrate]

A substrate having a flat surface can be used as the substrate includedin the touch panel. The substrate on the side from which light from thedisplay element is extracted is formed using a material that transmitsthe light. For example, a material such as glass, quartz, ceramics,sapphire, or an organic resin can be used.

The weight and thickness of the touch panel can be decreased by using athin substrate. A flexible touch panel can be obtained by using asubstrate that is thin enough to have flexibility.

As the glass, for example, non-alkali glass, barium borosilicate glass,aluminoborosilicate glass, or the like can be used.

Examples of a material that has flexibility and transmits visible lightinclude flexible glass, polyester resins such as polyethyleneterephthalate (PET) and polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, a polyvinyl chloride resin, and a polytetrafluoroethylene(PTFE). In particular, a material whose thermal expansion coefficient islow is preferable, and for example, a polyamide imide resin, a polyimideresin, or PET can be suitably used. A substrate in which a glass fiberis impregnated with an organic resin or a substrate whose thermalexpansion coefficient is reduced by mixing an organic resin with aninorganic filler can also be used. A substrate using such a material islightweight, and accordingly a touch panel using this substrate can alsobe lightweight.

Since it is not necessary for the substrate through which light emissionis not extracted to have a light-transmitting property, a metalsubstrate, a ceramic substrate, a semiconductor substrate, or the likecan be used as well as the above-described substrates. A metal materialand an alloy material, which have high thermal conductivity, ispreferable because they can easily conduct heat to the whole sealingsubstrate and accordingly can prevent a local temperature rise in thetouch panel. To obtain flexibility and bendability, the thickness of ametal substrate is preferably greater than or equal to 10 μm and lessthan or equal to 200 μm, more preferably greater than or equal to 20 μmand less than or equal to 50 μm.

Although there is no particular limitation on a material of a metalsubstrate, it is favorable to use, for example, a metal such asaluminum, copper, and nickel, an aluminum alloy, or an alloy such asstainless steel.

It is preferable to use a substrate subjected to insulation treatment,e.g., a metal substrate whose surface is oxidized or provided with aninsulating film. An insulating film may be formed by, for example, acoating method such as a spin-coating method and a dipping method, anelectrodeposition method, an evaporation method, or a sputtering method.An oxide film may be formed over the substrate surface by an anodicoxidation method, exposing to or heating in an oxygen atmosphere, or thelike.

A hard coat layer (e.g., a silicon nitride layer) by which a touch panelsurface is protected from damage, a layer (e.g., an aramid resin layer)that can disperse pressure, or the like may be stacked over the flexiblesubstrate. Furthermore, to suppress a decrease in lifetime of thedisplay element due to moisture and the like, an insulating film withlow water permeability may be stacked over the flexible substrate. Forexample, an inorganic insulating material such as silicon nitride,silicon oxynitride, aluminum oxide, or aluminum nitride can be used.

The substrate may be formed by stacking a plurality of layers. When aglass layer is used, a barrier property against water and oxygen can beimproved and thus a highly reliable touch panel can be provided.

A substrate in which a glass layer, an adhesive layer, and an organicresin layer are stacked from the side closer to the display element canbe used, for example. The thickness of the glass layer is greater thanor equal to 20 μm and less than or equal to 200 μm, preferably greaterthan or equal to 25 μm and less than or equal to 100 μm. With such athickness, the glass layer can have both a high barrier property againstwater and oxygen and a high flexibility. The thickness of the organicresin layer is greater than or equal to 10 μm and less than or equal to200 μm, preferably greater than or equal to 20 μm and less than or equalto 50 μm. Providing such an organic resin layer, occurrence of a crackor a break in the glass layer can be suppressed and mechanical strengthcan be improved. With the substrate that includes such a compositematerial of a glass material and an organic resin, a highly reliableflexible touch panel can be provided.

[Transistor]

The transistor includes a conductive layer functioning as the gateelectrode, the semiconductor layer, a conductive layer functioning asthe source electrode, a conductive layer functioning as the drainelectrode, and an insulating layer functioning as the gate insulatinglayer. The above description is that of the case where a bottom-gatetransistor is used.

Note that there is no particular limitation on the structure of thetransistor included in the touch panel of one embodiment of the presentinvention. For example, a forward staggered transistor or an invertedstaggered transistor may be used. A top-gate transistor or a bottom-gatetransistor may be used. There is no particular limitation on asemiconductor material that is used for the transistor, and for example,an oxide semiconductor, silicon, or germanium can be used.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle-crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. It is preferable that a semiconductorhaving crystallinity be used, in which case deterioration of thetransistor characteristics can be suppressed.

As a semiconductor material for the semiconductor layer of thetransistor, an element of Group 14, a compound semiconductor, or anoxide semiconductor can be used, for example. Typically, a semiconductorcontaining silicon, a semiconductor containing gallium arsenide, anoxide semiconductor containing indium, or the like can be used.

In particular, an oxide semiconductor having a wider band gap thansilicon is preferably used. A semiconductor material having a wider bandgap and a lower carrier density than silicon is preferably used becauseoff-state leakage current of the transistor can be reduced.

For example, at least indium (In) or zinc (Zn) is preferably included asthe oxide semiconductor. More preferably, an In-M-Zn-based oxide (M is ametal such as Al, Ti, Ga, Ge, Y, Zr, Sn, La, Ce, or Hf) is included.

As the semiconductor layer, it is particularly preferable to use anoxide semiconductor film including a plurality of crystal parts whosec-axes are aligned substantially perpendicular to a surface on which thesemiconductor layer is formed or the top surface of the semiconductorlayer and in which a grain boundary is not observed between adjacentcrystal parts.

There is no grain boundary in such an oxide semiconductor; therefore,generation of a crack in an oxide semiconductor film which is caused bystress when a display panel is bent is prevented. Therefore, such anoxide semiconductor can be preferably used for a flexible touch panelwhich is used in a bent state, or the like.

Moreover, the use of such an oxide semiconductor with crystallinity forthe semiconductor layer makes it possible to provide a highly reliabletransistor in which a change in the electrical characteristics issuppressed.

A transistor with an oxide semiconductor whose band gap is larger thanthe band gap of silicon can hold charges stored in a capacitor that isseries-connected to the transistor for a long time, owing to the lowoff-state current of the transistor. When such a transistor is used fora pixel, operation of a driver circuit can be stopped while a gray scaleof an image displayed in each display region is maintained. As a result,a display device with extremely low power consumption can be obtained.

The semiconductor layer preferably includes, for example, a filmrepresented by an In-M-Zn oxide that contains at least indium, zinc, andM (a metal such as Al, Ti, Ga, Y, Zr, La, Ce, Sn, or Hf). In order toreduce variations in electrical characteristics of the transistorincluding the oxide semiconductor, the oxide semiconductor preferablycontains a stabilizer in addition to indium, zinc, and M.

Examples of the stabilizer, including metals that can be used as M, aregallium, tin, hafnium, aluminum, and zirconium. As another stabilizer,lanthanoid such as lanthanum, cerium, praseodymium, neodymium, samarium,europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium,ytterbium, or lutetium can be given.

As an oxide semiconductor included in the semiconductor layer, any ofthe following can be used, for example: an In—Ga—Zn-based oxide, anIn—Al—Zn-based oxide, an In—Sn—Zn-based oxide, an In—Hf—Zn-based oxide,an In—La—Zn-based oxide, an In—Ce—Zn-based oxide, an In—Pr—Zn-basedoxide, an In—Nd—Zn-based oxide, an In—Sm—Zn-based oxide, anIn—Eu—Zn-based oxide, an In—Gd—Zn-based oxide, an In—Tb—Zn-based oxide,an In—Dy—Zn-based oxide, an In—Ho—Zn-based oxide, an In—Er—Zn-basedoxide, an In—Tm—Zn-based oxide, an In—Yb—Zn-based oxide, anIn—Lu—Zn-based oxide, an In—Sn—Ga—Zn-based oxide, an In—Hf—Ga—Zn-basedoxide, an In—Al—Ga—Zn-based oxide, an In—Sn—Al—Zn-based oxide, anIn—Sn—Hf—Zn-based oxide, and an In—Hf—Al—Zn-based oxide.

Note that here, for example, an “In—Ga—Zn-based oxide” means an oxidecontaining In, Ga, and Zn as its main components, and there is nolimitation on the ratio of In:Ga:Zn. The In—Ga—Zn-based oxide maycontain another metal element in addition to In, Ga, and Zn.

The semiconductor layer and the conductive layer may include the samemetal elements contained in the above oxides. The use of the same metalelements for the semiconductor layer and the conductive layer can reducethe manufacturing cost. For example, when metal oxide targets with thesame metal composition are used, the manufacturing cost can be reduced,and the same etching gas or the same etchant can be used in processingthe semiconductor layer and the conductive layer. Note that even whenthe semiconductor layer and the conductive layer include the same metalelements, they have different compositions in some cases. For example, ametal element in a film is released during the manufacturing process ofthe transistor and the capacitor, which might result in different metalcompositions.

In the case where the semiconductor layer is an In-M-Zn oxide, theproportions of In and M when the summation of In and M is assumed to be100 atomic % are preferably as follows: the atomic percentage of In ishigher than 25 atomic % and the atomic percentage of M is lower than 75atomic %, more preferably, the atomic percentage of In is higher than 34atomic % and the atomic percentage of M is lower than 66 atomic %.

The energy gap of the semiconductor layer is 2 eV or more, preferably2.5 eV or more, more preferably 3 eV or more. With the use of an oxidesemiconductor having such a wide energy gap, the off-state current ofthe transistor can be reduced.

The thickness of the semiconductor layer is greater than or equal to 3nm and less than or equal to 200 nm, preferably greater than or equal to3 nm and less than or equal to 100 nm, more preferably greater than orequal to 3 nm and less than or equal to 50 nm.

In the case where the semiconductor layer contains an In-M-Zn oxide (Mrepresents Al, Ga, Y, Zr, La, Ce, or Nd), it is preferable that theatomic ratio of metal elements of a sputtering target used for forming afilm of the In-M-Zn oxide satisfy In M and Zn≥M. As the atomic ratio ofmetal elements of such a sputtering target, In:M:Zn=1:1:1,In:M:Zn=1:1:1.2, and In:M:Zn=3:1:2 are preferable. Note that the atomicratio of metal elements in the formed semiconductor layer varies fromthe above atomic ratio of metal elements of the sputtering target withina range of ±40% as an error.

An oxide semiconductor film with low carrier density is used as thesemiconductor layer. For example, the semiconductor layer is an oxidesemiconductor with low carrier density (specifically, lower than orequal to 1×10¹⁷/cm³, preferably lower than or equal to 1×10¹⁵/cm³, morepreferably lower than or equal to 1×10¹³/cm³, still more preferablylower than or equal to 1×10¹¹/cm³, even more preferably lower than1×10¹⁰/cm³, and higher than or equal to 1×10⁻⁹/cm³). Such an oxidesemiconductor is referred to as a highly purified intrinsic orsubstantially highly purified intrinsic oxide semiconductor. The oxidesemiconductor has low impurity concentration and a low density of defectstates and can thus be referred to as an oxide semiconductor havingstable characteristics.

Note that, without limitation to those described above, a material withan appropriate composition may be used depending on requiredsemiconductor characteristics and electrical characteristics (e.g.,field-effect mobility and threshold voltage) of a transistor. To obtainthe required semiconductor characteristics of the transistor, it ispreferable that the carrier density, the impurity concentration, thedefect density, the atomic ratio between a metal element and oxygen, theinteratomic distance, the density, and the like of the semiconductorlayer be set to appropriate values.

When silicon or carbon that is one of elements belonging to Group 14 iscontained in the semiconductor layer, oxygen vacancies are increased inthe semiconductor layer, and the semiconductor layer becomes n-type.Thus, the concentration of silicon or carbon (measured by secondary ionmass spectrometry (SIMS)) in the semiconductor layer is lower than orequal to 2×10¹⁸ atoms/cm³, preferably lower than or equal to 2×10¹⁷atoms/cm³.

An alkali metal and an alkaline earth metal might generate carriers whenbonded to an oxide semiconductor, in which case the off-state current ofthe transistor might be increased. Therefore, the concentration ofalkali metal or alkaline earth metal of the semiconductor layer, whichis measured by SIMS, is lower than or equal to 1×10¹⁸ atoms/cm³,preferably lower than or equal to 2×10¹⁶ atoms/cm³.

When nitrogen is contained in the semiconductor layer, electrons servingas carriers are generated and the carrier density increases, so that thesemiconductor layer easily becomes n-type. Thus, a transistor includingan oxide semiconductor which contains nitrogen is likely to be normallyon. For this reason, the concentration of nitrogen which is measured bySIMS is preferably set to, for example, lower than or equal to 5×10¹⁸atoms/cm³.

The semiconductor layer may have, for example, a non-single crystalstructure. Examples of the non-single crystal structure include a c-axisaligned crystalline oxide semiconductor (CAAC-OS), a polycrystallinestructure, a microcrystalline structure, and an amorphous structure.Among the non-single crystal structures, the amorphous structure has thehighest density of defect states, whereas CAAC-OS has the lowest densityof defect states.

The semiconductor layer may have an amorphous structure, for example.The oxide semiconductor film having an amorphous structure hasdisordered atomic arrangement and no crystalline component, for example.Alternatively, the oxide film having an amorphous structure has, forexample, an absolutely amorphous structure and no crystal part.

Note that the semiconductor layer may be a mixed film including two ormore of the following: a region having an amorphous structure, a regionhaving a microcrystalline structure, a region having a polycrystallinestructure, a CAAC-OS region, and a region having a single-crystalstructure. The mixed film includes, for example, two or more of a regionhaving an amorphous structure, a region having a microcrystallinestructure, a region having a polycrystalline structure, a CAAC-OSregion, and a region having a single-crystal structure in some cases.The mixed film may have a stacked-layer structure of two or more of thefollowing: a region having an amorphous structure, a region having amicrocrystalline structure, a region having a polycrystalline structure,a CAAC-OS region, and a region having a single-crystal structure.

Alternatively, silicon is preferably used as a semiconductor in which achannel of a transistor is formed. Although amorphous silicon may beused as silicon, silicon having crystallinity is particularlypreferable. For example, microcrystalline silicon, polycrystallinesilicon, single-crystal silicon, or the like is preferably used. Inparticular, polycrystalline silicon can be formed at a lower temperaturethan single-crystal silicon and has higher field effect mobility andhigher reliability than amorphous silicon. When such a polycrystallinesemiconductor is used for a pixel, the aperture ratio of the pixel canbe improved. Even in the case of a high-definition display panel, a gatedriver circuit and a source driver circuit can be formed over asubstrate over which the pixels are formed, and the number of componentsof an electronic device can be reduced.

[Conductive Layer]

As a gate, a source, and a drain of a transistor, and a wiring or anelectrode included in a touch panel, any of metals such as aluminum,titanium, chromium, nickel, copper, yttrium, zirconium, molybdenum,silver, tantalum, and tungsten, or an alloy containing any of thesemetals as its main component can be used. A single-layer structure ormulti-layer structure including a film containing any of these materialscan be used. For example, the following structures can be given: asingle-layer structure of an aluminum film containing silicon, atwo-layer structure in which an aluminum film is stacked over a titaniumfilm, a two-layer structure in which an aluminum film is stacked over atungsten film, a two-layer structure in which a copper film is stackedover a copper-magnesium-aluminum alloy film, a two-layer structure inwhich a copper film is stacked over a titanium film, a two-layerstructure in which a copper film is stacked over a tungsten film, athree-layer structure in which a titanium film or a titanium nitridefilm, an aluminum film or a copper film, and a titanium film or atitanium nitride film are stacked in this order, and a three-layerstructure in which a molybdenum film or a molybdenum nitride film, analuminum film or a copper film, and a molybdenum film or a molybdenumnitride film are stacked in this order. Note that an oxide such asindium oxide, tin oxide, or zinc oxide may be used. Copper containingmanganese is preferably used because controllability of a shape byetching is increased.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zincoxide to which gallium is added, or graphene can be used. Alternatively,a metal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium, or an alloy material containing any of these metal materialscan be used. Alternatively, a nitride of the metal material (e.g.,titanium nitride) or the like may be used. In the case of using themetal material or the alloy material (or the nitride thereof), thethickness is set small enough to be able to transmit light.Alternatively, a stack of any of the above materials can be used as theconductive layer. For example, a stacked film of indium tin oxide and analloy of silver and magnesium is preferably used because theconductivity can be increased.

Alternatively, for the conductive layer, an oxide semiconductor similarto that of the semiconductor layer is preferably used. In that case, itis preferable that the conductive layer be formed to have a lowerelectric resistance than a region in the semiconductor layer where achannel is formed.

For example, such a conductive layer can be used as the conductive layer223 functioning as the second gate electrode of the transistor.Alternatively, it can be used as another light-transmitting conductivelayer.

<Method for Controlling Resistivity of Oxide Semiconductor>

An oxide semiconductor film that can be used as each of thesemiconductor layer and the conductive layer includes a semiconductormaterial whose resistivity can be controlled by oxygen vacancies in thefilm and/or the concentration of impurities such as hydrogen or water inthe film. Thus, treatment to be performed on the semiconductor layer andthe conductive layer is selected from the following to control theresistivity of each of the oxide semiconductor films: treatment forincreasing oxygen vacancies and/or impurity concentration and treatmentfor reducing oxygen vacancies and/or impurity concentration.

Specifically, plasma treatment is performed on the oxide semiconductorfilm used as the conductive layer to increase oxygen vacancies and/orimpurities such as hydrogen or water in the oxide semiconductor film, sothat the oxide semiconductor film can have a high carrier density andlow resistivity. Furthermore, an insulating film containing hydrogen isformed in contact with the oxide semiconductor film to diffuse hydrogenfrom the insulating film containing hydrogen to the oxide semiconductorfilm, so that the oxide semiconductor film can have a high carrierdensity and low resistivity.

The semiconductor layer that functions as the channel region of thetransistor is not in contact with the insulating films containinghydrogen. With the use of an insulating film containing oxygen, in otherwords, an insulating film capable of releasing oxygen for at least oneof the insulating films, oxygen can be supplied to the semiconductorlayer. The semiconductor layer to which oxygen is supplied has highresistivity because oxygen vacancies in the film or at the interface arecompensated. Note that as the insulating film capable of releasingoxygen, a silicon oxide film or a silicon oxynitride film can be used,for example.

In order to reduce the resistivity of the oxide semiconductor film, anion implantation method, an ion doping method, a plasma immersion ionimplantation method, or the like can be employed to inject hydrogen,boron, phosphorus, or nitrogen into the oxide semiconductor film.

In order to reduce the resistivity of the oxide semiconductor film,plasma treatment may be performed on the oxide semiconductor film. Forthe plasma treatment, a gas containing at least one of a rare gas (He,Ne, Ar, Kr, or Xe), hydrogen, and nitrogen is typically used.Specifically, plasma treatment in an Ar atmosphere, plasma treatment ina mixed gas atmosphere of Ar and hydrogen, plasma treatment in anammonia atmosphere, plasma treatment in a mixed gas atmosphere of Ar andammonia, plasma treatment in a nitrogen atmosphere, or the like can beemployed.

In the oxide semiconductor film subjected to the plasma treatment, anoxygen vacancy is formed in a lattice from which oxygen is released (orin a portion from which oxygen is released). This oxygen vacancy cancause carrier generation. When hydrogen is supplied from an insulatingfilm that is in the vicinity of the oxide semiconductor film(specifically, an insulating film that is in contact with the lowersurface or the upper surface of the oxide semiconductor film), andhydrogen is bonded to the oxygen vacancy, an electron serving as acarrier might be generated.

The oxide semiconductor film in which oxygen vacancies are compensatedwith oxygen and the hydrogen concentration is reduced can be referred toas a highly purified intrinsic or substantially highly purifiedintrinsic oxide semiconductor film. Here, the term “substantiallyintrinsic” refers to a state where an oxide semiconductor film has acarrier density of lower than 8×10¹¹/cm³, preferably lower than1×10¹¹/cm³, more preferably lower than 1×10¹⁰/cm³. A highly purifiedintrinsic or substantially highly purified intrinsic oxide semiconductorfilm has few carrier generation sources and can thus have a low carrierdensity. The highly purified intrinsic or substantially highly purifiedintrinsic oxide semiconductor film has a low density of defect statesand can accordingly have a low density of trap states.

The highly purified intrinsic or substantially highly purified intrinsicoxide semiconductor film has an extremely low off-state current; evenwhen an element has a channel width of 1×10⁶ μm and a channel length of10 μm, the off-state current can be lower than or equal to themeasurement limit of a semiconductor parameter analyzer, i.e., lowerthan or equal to 1×10⁻¹³ A, at a voltage (drain voltage) between asource electrode and a drain electrode ranging from 1 V to 10 V.Accordingly, the transistor in which the channel region is formed in thesemiconductor layer that is a highly purified intrinsic or substantiallyhighly purified intrinsic oxide semiconductor film can have a smallvariation in electrical characteristics and high reliability.

For example, an insulating film containing hydrogen, in other words, aninsulating film capable of releasing hydrogen, typically, a siliconnitride film, is used as the insulating film in contact with the oxidesemiconductor film used as the conductive layer, whereby hydrogen can besupplied to the conductive layer. The hydrogen concentration of theinsulating film capable of releasing hydrogen is preferably higher thanor equal to 1×10²² atoms/cm³. Such an insulating film is formed incontact with the conductive layer, whereby hydrogen can be effectivelycontained in the conductive layer. In this manner, the resistivity ofthe oxide semiconductor film can be controlled by changing the structureof insulating films in contact with the semiconductor layer and theconductive layer.

Hydrogen contained in the oxide semiconductor film reacts with oxygenbonded to a metal atom to be water, and in addition, an oxygen vacancyis formed in a lattice from which oxygen is released (or in a portionfrom which oxygen is released). Due to entry of hydrogen into the oxygenvacancy, an electron serving as a carrier is generated in some cases.Furthermore, bonding of part of hydrogen to oxygen bonded to a metalatom causes generation of an electron serving as a carrier in somecases. Accordingly, the conductive layer formed in contact with theinsulating film containing hydrogen is an oxide semiconductor film thathas a higher carrier density than the semiconductor layer.

In the semiconductor layer where the channel region of the transistor isformed, it is preferable to reduce hydrogen as much as possible.Specifically, in the semiconductor layer, the hydrogen concentrationwhich is measured by SIMS is set to lower than or equal to 2×10²⁰atoms/cm³, preferably lower than or equal to 5×10¹⁹ atoms/cm³, morepreferably lower than or equal to 1×10¹⁹ atoms/cm³, more preferablylower than 5×10¹⁸ atoms/cm³, more preferably lower than or equal to1×10¹⁸ atoms/cm³, more preferably lower than or equal to 5×10¹⁷atoms/cm³, more preferably lower than or equal to 1×10¹⁶ atoms/cm³.

The conductive layer is an oxide semiconductor film that has a higherhydrogen concentration and/or a larger number of oxygen vacancies (i.e.,a lower resistivity) than the semiconductor layer. The hydrogenconcentration in the conductive layer is higher than or equal to 8×10¹⁹atoms/cm³, preferably higher than or equal to 1×10²⁰ atoms/cm³, morepreferably higher than or equal to 5×10²⁰ atoms/cm³. The hydrogenconcentration in the conductive layer is greater than or equal to 2times, preferably greater than or equal to 10 times the hydrogenconcentration in the semiconductor layer. The resistivity of theconductive layer is preferably greater than or equal to 1×10⁻⁸ times andless than 1×10⁻¹ times the resistivity of the semiconductor layer. Theresistivity of the conductive layer is typically higher than or equal to1×10⁻³ Ω/cm and lower than 1×10⁴ Ωcm, preferably higher than or equal to1×10⁻³ Ωcm and lower than 1×10⁻¹ Ωcm.

[Insulating Layer]

Examples of an insulating material that can be used for the insulatinglayers, the overcoat, the spacer, and the like include a resin such asacrylic or epoxy resin, a resin having a siloxane bond, and an inorganicinsulating material such as silicon oxide, silicon oxynitride, siliconnitride oxide, silicon nitride, or aluminum oxide.

[Adhesive Layer]

For the adhesive layers, a curable resin such as a heat curable resin, aphotocurable resin, or a two-component type curable resin can be used.For example, an acrylic resin, a urethane resin, an epoxy resin, or aresin having a siloxane bond such as silicone can be used.

[Connection Layer]

As the connection layers, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

[Coloring Layer]

As examples of a material that can be used for the coloring layers, ametal material, a resin material, and a resin material containing apigment or dye can be given.

The above is the description of each of the components.

[Structural Example of Touch Sensor]

Next, a structure example of the touch sensor 22 which can be used forthe touch panel module 10 of one embodiment of the present invention isdescribed with reference to drawings.

FIG. 9A is a schematic top view (schematic plan view) of part of thetouch sensor 22. FIG. 9B is an enlarged schematic top view of a regionsurrounded by dashed-dotted line in FIG. 9A.

As shown in FIGS. 9A and 9B, it is preferable that the conductive layer23 be partly narrowed so that the width of a portion crossing theconductive layer 25 is small. Thus, the capacitance of the capacitor 11can be reduced. In the case of using a self-capacitive touch sensor, thedetection sensitivity can be increased more as the capacitance of thecapacitor 11 is smaller.

Furthermore, between the conductive layer 23 and the conductive layer 24which are adjacent to each other, a conductive layer 26 which iselectrically insulated from these conductive layers 23 and 24 may beprovided. The conductive layer 26 can suppress the formation of a thinportion of the touch sensor 22. For example, in the case where theconductive layer 23 and the conductive layer 24 are formed over the sameflat surface, the conductive layer 26 formed in a manner similar to thatof the conductive layer 23 and the conductive layer 24 can increasecoverage of a thin film formed after the formation of these conductivelayers; thus, a surface can be planarized. Furthermore, owing to theuniform thickness of the touch sensor 22, luminance unevenness of lightemitted from the pixels through the touch sensor 22 can be reduced, sothat the touch panel can achieve high display quality.

FIG. 9C shows the case where the conductive layer 23 and the conductivelayer 24 are formed over different flat surfaces and the conductivelayer 25 is not provided. At this time, the conductive layer 26 may beformed over the flat surface over which the conductive layer 23 or theconductive layer 24 is formed, or may be formed over a flat surfacedifferent from the flat surface over which the conductive layer 23 orthe conductive layer 24 is formed. Note that the conductive layer 26 isnot necessarily provided if not necessary.

FIG. 10A shows an example of a circuit diagram of the touch sensor 22including a plurality of conductive layers 23 and a plurality ofconductive layers 24. In FIG. 10A, six conductive layers 23 and sixconductive layers 24 are shown for simplicity, but the number of theconductive layers 23 and the number of the conductive layers 24 are notlimited thereto.

One capacitor 11 is formed between one of the conductive layers 23 andone of the conductive layers 24. Therefore, capacitors 11 are arrangedin a matrix.

In the case of a projected self-capacitive type, a pulse voltage isapplied to each of the conductive layers 23 and 24 so that theconductive layers 23 and 24 are scanned, and the value of a currentflowing in the conductive layer 23 or the conductive layer 24 at thistime is sensed. The amount of current is changed when an objectapproaches, and therefore, positional information of the object can beobtained by sensing the difference between the values. In the case of aprojected mutual-capacitive type, a pulse voltage is applied to one ofthe conductive layers 23 and 24 so that one of the conductive layers 23and 24 is scanned, and a current flowing in the other is sensed toobtain positional information of the object.

Each of the conductive layers 23 and 24 preferably has a lattice shapeor a mesh shape having a plurality of openings. FIG. 10B shows anexample of a top surface shape of part of the conductive layer 23.

The conductive layer 23 shown in FIG. 10B has a lattice shape in which adistance P1 is provided in a lateral direction and a distance P2 isprovided in a longitudinal direction. The distance P1 and the distanceP2 are almost the same in FIG. 10B, but may be different from eachother. For example, the distance P2 in a longitudinal direction may belarger than the distance P1 in a lateral direction as shown in FIG. 10C,or the distance P2 in a longitudinal direction may be smaller than thedistance P1 in a lateral direction. The same can be said for theconductive layer 24.

The aperture ratio of the conductive layer 23 or the conductive layer 24(the proportion of the opening area in the conductive layer 23 or theconductive layer 24 per unit area) is preferably higher than or equal to20% and lower than 100%, more preferably higher than or equal to 30% andlower than 100%, still more preferably higher than or equal to 50% andlower than 100% in a region.

The aperture ratio can be easily calculated from the distance P1, thedistance P2, and the width of the conductive layer. Alternatively, whena region R is assumed to be a periodic unit in FIG. 10B, the apertureratio can be calculated from the ratio of the area of the region R tothe area of the conductive layer 23 included in the region R. Here, theregion R is a periodic unit of a periodic pattern of the conductivelayer 23. By arranging regions R longitudinally and laterally in aperiodic manner, the pattern of the conductive layer 23 can be formed.

In each of the conductive layer 23 and the conductive layer 24, the linewidth of a lattice is preferably greater than or equal to 50 nm and lessthan or equal to 100 μm, more preferably greater than or equal to 1 μmand less than or equal to 50 μm, still more preferably greater than orequal to 1 μm and less than or equal to 20 μm. The lattice having such anarrow line width allows adjacent pixels to be close to each other inthe case where the opening overlaps with the pixel as described later.Consequently, the touch panel can have higher resolution and higheraperture ratio.

FIG. 11A is an enlarged schematic top view of a boundary portion betweenthe conductive layer 23 and the conductive layer 24.

Each of the conductive layers 23 and 24 preferably has a lattice shape(also referred to as a mesh shape). That is, each of the conductivelayers 23 and 24 preferably has a plurality of openings (an opening 23 aand an opening 24 a). When the opening and the pixel are provided tooverlap with each other as described later, light emitted from thedisplay element in the pixel is not blocked by the conductive layer 23and the conductive layer 24, or a reduction in the luminance of lightdue to the transmission through the conductive layer 23 and theconductive layer 24 does not occur. As a result, the touch sensor 22 canbe used in the touch panel without a reduction in the aperture ratio ofthe pixel and the light extraction efficiency. It is preferable that theconductive layer 25 similarly have a shape not overlapping with thepixel.

As shown in FIG. 11A, an opening 22 a surrounded by part of theconductive layer 23 and part of the conductive layer 24 may be formed inthe boundary portion. Such a structure can significantly reduce thedistance between the conductive layer 23 and the conductive layer 24 andcan increase capacitance therebetween. In particular, in the case ofusing a mutual capacitive type, the distance between the two conductivelayers is preferably reduced to increase capacitance therebetween.

FIG. 11B is an enlarged schematic top view of an intersection of theconductive layers 23 and 24. An example where the two adjacentconductive layers 24 are electrically connected to each other with theconductive layer 25 is shown here. Although not illustrated in thedrawing, the insulating layer 121 is provided between the conductivelayer 25 and the conductive layers 23 and 24. The conductive layers 24and 25 are electrically connected to each other through an openingprovided in the insulating layer 121. The conductive layers 23 and 25partly overlap with each other with the insulating layer 121 providedtherebetween.

[Arrangement Example of Opening of Conductive Layer and Pixel]

FIGS. 12A to 12G are schematic views each showing the positionalrelationship between a pixel, sub-pixels included in the pixel, and theconductive layer 23 which are seen from the display surface side. Notethat although the conductive layer 23 is shown in FIGS. 12A to 12G as anexample, the same applies to the conductive layer 24 and the conductivelayer 25.

In the example shown in FIG. 12A, the pixel 33 includes a sub-pixel 33R,a sub-pixel 33G, and a sub-pixel 33B. For example, the sub-pixel 33R,the sub-pixel 33G, and the sub-pixel 33B have a function of expressingred color, green color, and blue color, respectively. Note that thenumber and the colors of the sub-pixels included in the pixel 33 are notlimited thereto.

The sub-pixels included in the pixel 33 each have a display element. Theabove-described reflective liquid crystal element can be used as thedisplay element. Besides the reflective liquid crystal element, examplesof the display element include light-emitting elements such as organicEL elements; transmissive or semi-transmissive liquid crystal elements;display elements (electronic ink) that perform display by anelectrophoretic method, an electronic liquid powder (registeredtrademark) method, or the like; MEMS shutter display elements; andoptical interference type MEMS display elements. The sub-pixel may havea transistor, a capacitor, a wiring that electrically connects thetransistor and the capacitor, and the like in addition to the displayelement.

In the structure shown in FIG. 12A, each of a plurality of openings inthe conductive layer 23 is provided to overlap with the threesub-pixels, i.e., the sub-pixel 33R, the sub-pixel 33G, and thesub-pixel 33B. In this manner, the opening in the conductive layer 23 ispreferably provided to overlap with one sub-pixel.

As shown in FIG. 12A, it is preferable that there is no gap between theconductive layer 23 and each sub-pixel because light leakage from thesub-pixels can be suppressed. For example, the conductive layer 23 isprovided to overlap with an end portion of the coloring layer of asub-pixel or an end portion of a pixel electrode; thus, the conductivelayer 23 can be provided so that such a gap is not formed. Furthermore,with such a structure, a surface area of the conductive layer 23 can beincreased, so that wiring resistance of the conductive layer 23 can bereduced and the detection sensitivity can be increased.

FIG. 12B illustrates a structure where the conductive layer 23 isprovided between two adjacent sub-pixels exhibiting different colors.Since color mixture does not occur between two adjacent sub-pixelsexhibiting the same color, a structure including a portion where theconductive layer 23 is not provided therebetween as illustrated in FIG.12B may be employed.

FIGS. 12C and 12D each show an example where the pixel 33 furtherincludes a sub-pixel 33Y in the structure shown in FIGS. 12A and 12B.For example, a pixel capable of expressing yellow color can be used forthe sub-pixel 33Y. Instead of the sub-pixel 33Y, a pixel capable ofexpressing white color may be used. When the pixel 33 includessub-pixels of more than three colors, power consumption can be reduced.

In the examples shown in FIGS. 12A to 12D, sub-pixels of each color arearranged in a stripe pattern. Alternatively, as shown in FIG. 12E,sub-pixels of two colors may be alternated in one direction, forexample.

Furthermore, the sub-pixels included in the pixel 33 may differ in size(e.g., the area of a region contributing to display). For example, thesize of the sub-pixel of blue color with a relatively low luminosityfactor can be set large, whereas the size of the sub-pixel of green orred color with a relatively high luminosity factor can be set small.

FIGS. 12F and 12G each show an example where the size of the sub-pixel33B is larger than the size of the sub-pixel 33R and the size of thesub-pixel 33G. In the examples shown here, the sub-pixel 33R and thesub-pixel 33G are alternated. However, sub-pixels of each color may bearranged in a stripe pattern as shown in FIG. 12A and other drawings,and may have different sizes from each other.

Note that although the positional relationship between the conductivelayer 23 and the sub-pixels is described here, the same applies to theconductive layer 24 and the conductive layer 25. That is, in the touchpanel of one embodiment of the present invention, the opening 23 a inthe conductive layer 23 overlaps with one or more sub-pixels in a regionand the opening 24 a in the conductive layer 24 overlaps with one ormore of the other sub-pixels in a region. Since each sub-pixel includesthe display element as described above, it can be said that the opening23 a and the opening 24 a each have a region overlapping with one ormore display elements.

At least part of this embodiment can be implemented in combination withany of the embodiments described in this specification as appropriate.

Embodiment 2

In this embodiment, examples of a driving method of an input device oran input/output device of one embodiment of the present invention aredescribed with reference to drawings.

[Example of Sensing Method of Sensor]

FIG. 13A is a block diagram illustrating the structure of a mutualcapacitive touch sensor. FIG. 13A illustrates a pulse voltage outputcircuit 601 and a current sensing circuit 602. Note that in FIG. 13A,six wirings X1 to X6 represent electrodes 621 to which a pulse voltageis applied, and six wirings Y1 to Y6 represent electrodes 622 that sensechanges in current. FIG. 13A also illustrates a capacitor 603 that isformed where electrodes 621 and 622 overlap with each other. Note thatfunctional replacement between the electrodes 621 and 622 is possible.

The pulse voltage output circuit 601 is a circuit for sequentiallyapplying a pulse voltage to the wirings X1 to X6. By application of apulse voltage to the wirings X1 to X6, an electric field is generatedbetween the electrodes 621 and 622 of the capacitor 603. When theelectric field between the electrodes is shielded, for example, a changeoccurs in mutual capacitance of the capacitor 603. The approach orcontact of an object can be sensed by utilizing this change.

The current sensing circuit 602 is a circuit for sensing changes incurrent flowing through the wirings Y1 to Y6 that are caused by thechange in capacitance in the capacitor 603. No change in current valueis sensed in the wirings Y1 to Y6 when there is no approach or contactof an object, whereas a decrease in current value is sensed whencapacitance is decreased owing to the approach or contact of an object.Note that an integrator circuit or the like is used for sensing ofcurrent values.

FIG. 13B is a timing chart showing input and output waveforms in themutual capacitive touch sensor illustrated in FIG. 13A. In FIG. 13B,detection of an object is performed in all the rows and columns in oneframe period. FIG. 13B shows a period when an object is not detected(not touched) and a period when an object is detected (touched). Sensedcurrent values of the wirings Y1 to Y6 are shown as waveforms of voltagevalues.

A pulse voltage is sequentially applied to the wirings X1 to X6, andwaveforms of the wirings Y1 to Y6 change in accordance with the pulsevoltage. When there is no proximity or contact of an object, thewaveforms of the wirings Y1 to Y6 change in accordance with changes inthe voltages of the wirings X1 to X6. The current value is decreased atthe point of approach or contact of the object and accordingly thewaveform of the voltage value changes.

By sensing a change in mutual capacitance in this manner, proximity orcontact of an object can be sensed.

It is preferable that the pulse voltage output circuit 601 and thecurrent sensing circuit 602 be mounted on a substrate in a housing of anelectronic appliance or on the touch panel in the form of an IC. In thecase where the touch panel has flexibility, parasitic capacitance mightbe increased in a bent portion of the touch panel, and the influence ofnoise might be increased. In view of this, it is preferable to use an ICto which a driving method less influenced by noise is applied. Forexample, it is preferable to use an IC to which a driving method capableof increasing a signal-noise ratio (SN ratio) is applied.

Although FIG. 13A is a passive matrix type touch sensor in which onlythe capacitor 603 is provided at the intersection portion of wirings asa touch sensor, an active matrix type touch sensor including atransistor and a capacitor may be used. FIG. 14 is a sensor circuitincluded in an active matrix type touch sensor.

The sensor circuit includes the capacitor 603 and transistors 611, 612,and 613. A signal G2 is input to a gate of the transistor 613. A voltageVRES is applied to one of a source and a drain of the transistor 613,and one electrode of the capacitor 603 and a gate of the transistor 611are electrically connected to the other of the source and the drain ofthe transistor 613. One of a source and a drain of the transistor 611 iselectrically connected to one of a source and a drain of the transistor612, and a voltage VSS is applied to the other of the source and thedrain of the transistor 611. A signal G1 is input to a gate of thetransistor 612, and a wiring ML is electrically connected to the otherof the source and the drain of the transistor 612. The voltage VSS isapplied to the other electrode of the capacitor 603.

Next, the operation of the sensor circuit will be described. First, apotential for turning on the transistor 613 is supplied as the signalG2, and a potential with respect to the voltage VRES is thus applied tothe node n connected to the gate of the transistor 611. Then, apotential for turning off the transistor 613 is applied as the signalG2, whereby the potential of the node n is maintained.

Then, capacitance of the capacitor 603 changes owing to the approach orcontact of an object such as a finger, and accordingly the potential ofthe node n is changed from VRES.

In reading operation, a potential for turning on the transistor 612 issupplied as the signal G1. A current flowing through the transistor 611,that is, a current flowing through the wiring ML is changed inaccordance with the potential of the node n. By sensing this current,the approach or contact of an object can be detected.

It is preferable that the transistors 611, 612, and 613 each include anoxide semiconductor in a semiconductor layer where a channel is formed.In particular, such a transistor is preferably used as the transistor613 so that the potential of the node n can be held for a long time andthe frequency of operation of resupplying VRES to the node n (refreshoperation) can be reduced.

[Structure Example of in-Cell Touch Panel]

Although the examples where the electrodes in the touch sensor areformed over a substrate different from a substrate where the displayelement and the like are provided are described above, one or both ofthe pair of electrodes in the touch sensor may be formed over thesubstrate where the display element and the like are provided.

A structure example of a touch panel incorporating the touch sensor intoa display portion including a plurality of pixels is described below.Here, an example where a liquid crystal element is used as a displayelement provided in the pixel is shown.

FIG. 15A is an equivalent circuit diagram of part of a pixel circuitprovided in the display portion of the touch panel in this structureexample.

Each pixel includes at least a transistor 3503 and a liquid crystalelement 3504. In addition, a gate of the transistor 3503 is electricallyconnected to a wiring 3501, and one of a source and a drain of thetransistor 3503 is electrically connected to a wiring 3502.

The pixel circuit includes a plurality of wirings extending in the Xdirection (e.g., a wiring 3510_1 and a wiring 3510_2) and a plurality ofwirings extending in the Y direction (e.g., a wiring 3511). Thesewirings are provided to intersect with each other, and capacitance isformed therebetween.

Among the pixels provided in the pixel circuit, electrodes on one sideof the liquid crystal elements of some pixels adjacent to each other areelectrically connected to each other to form one block. The block isclassified into two types: an island-shaped block (e.g., a block 3515_1or a block 3515_2) and a linear block (e.g., a block 3516) extending inthe Y direction. Note that only part of the pixel circuit is illustratedin FIGS. 15A and 15B, but actually, these two kinds of blocks arerepeatedly arranged in the X direction and the Y direction.

The wiring 3510_1 (or the wiring 3510_2) extending in the X direction iselectrically connected to the island-shaped block 3515_1 (or the block3515_2). Although not illustrated, the wiring 3510_1 extending in the Xdirection is electrically connected to a plurality of island-shapedblocks 3515_1 which are provided discontinuously along the X directionwith the linear blocks therebetween. Furthermore, the wiring 3511extending in the Y direction is electrically connected to the linearblock 3516.

FIG. 15B is an equivalent circuit diagram illustrating the connectionbetween a plurality of wirings 3510 extending in the X direction and theplurality of wirings 3511 extending in the Y direction. An input voltageor a common potential can be input to each of the wirings 3510 extendingin the X direction. Furthermore, a ground potential can be input to eachof the wirings 3511 extending in the Y direction, or the wirings 3511can be electrically connected to the sensing circuit.

Operation of the above-described touch panel is described with referenceto FIGS. 16A and 16B.

Here, one frame period is divided into a writing period and a sensingperiod. The writing period is a period in which image data is written toa pixel, and the wirings 3501 (also referred to as gate lines or scanlines) illustrated in FIG. 15A are sequentially selected. On the otherhand, the sensing period is a period in which sensing is performed by atouch sensor, and the wirings 3510 extending in the X direction aresequentially selected and an input voltage is input.

FIG. 16A is an equivalent circuit diagram in the writing period. In thewriting period, a common potential is input to both the wiring 3510extending in the X direction and the wiring 3511 extending in the Ydirection.

FIG. 16B is an equivalent circuit diagram at a certain point of time inthe sensing period. In the sensing period, each of the wirings 3511extending in the Y direction is electrically connected to the sensingcircuit. An input voltage is input to the wirings 3510 extending in theX direction which are selected, and a common potential is input to thewirings 3510 extending in the X direction which are not selected.

Note that the driving method described here can be applied to not onlyan in-cell touch panel but also the above-described touch panels, andcan be used in combination with the method described in the drivingmethod example.

It is preferable that a period in which an image is written and a periodin which sensing is performed by a touch sensor be separately providedas described above. Thus, a decrease in sensitivity of the touch sensorcaused by noise generated when data is written to a pixel can besuppressed.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

Embodiment 3

In this embodiment, a display module and electronic devices that includethe display device of one embodiment of the present invention or adisplay system will be described with reference to FIG. 17 and FIGS. 18Ato 18H.

In a display module 8000 illustrated in FIG. 17, a touch panel 8004connected to an FPC 8003, a frame 8009, a printed board 8010, and abattery 8011 are provided between an upper cover 8001 and a lower cover8002.

The touch panel module of one embodiment of the present invention can beused for, for example, the touch panel 8004.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the size of the touchpanel 8004.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and may be formed so as to overlap with a display panel.Alternatively, a counter substrate (sealing substrate) of the touchpanel 8004 can have a touch panel function. Further alternatively, aphotosensor may be provided in each pixel of the touch panel 8004 toform an optical touch panel.

In the case of a transmissive liquid crystal element, a backlight 8007may be provided as illustrated in FIG. 17. The backlight 8007 includes alight source 8008. Although the light source 8008 is provided over thebacklight 8007 in FIG. 17, one embodiment of the present invention isnot limited to this structure. For example, a structure in which thelight source 8008 is provided at an end portion of the backlight 8007and a light diffusion plate is further provided may be employed. Notethat the backlight 8007 need not be provided in the case where aself-luminous light-emitting element such as an organic EL element isused or in the case where a reflective panel or the like is employed.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed board 8010. The frame 8009 can alsofunction as a radiator plate.

The printed board 8010 is provided with a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying power to the power supplycircuit, an external commercial power source or a power source using thebattery 8011 provided separately may be used. The battery 8011 can beomitted in the case of using a commercial power source.

The display module 8000 may be additionally provided with a componentsuch as a polarizing plate, a retardation plate, or a prism sheet.

FIGS. 18A to 18H illustrate electronic devices. These electronic devicescan include a housing 5000, a display portion 5001, a speaker 5003, anLED lamp 5004, operation keys 5005 (including a power switch or anoperation switch), a connection terminal 5006, a sensor 5007 (a sensorhaving a function of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), amicrophone 5008, and the like.

FIG. 18A illustrates a mobile computer, which can include a switch 5009,an infrared port 5010, and the like in addition to the above components.FIG. 18B illustrates a portable image reproducing device provided with arecording medium (e.g., a DVD reproducing device), which can include asecond display portion 5002, a recording medium read portion 5011, andthe like in addition to the above components. FIG. 18C illustrates agoggle-type display, which can include the second display portion 5002,a support 5012, an earphone 5013, and the like in addition to the abovecomponents. FIG. 18D illustrates a portable game machine, which caninclude the recording medium read portion 5011 and the like in additionto the above components. FIG. 18E illustrates a digital camera which hasa television reception function and can include an antenna 5014, ashutter button 5015, an imaging portion 5016, and the like in additionto the above components. FIG. 18F illustrates a portable game machine,which can include the second display portion 5002, the recording mediumread portion 5011, and the like in addition to the above components.FIG. 18G illustrates a portable television receiver, which can include acharger 5017 capable of transmitting and receiving signals, and the likein addition to the above components. FIG. 18H illustrates awrist-watch-type information terminal, which can include a band 5018, aclasp 5019, and the like in addition to the above components. Thedisplay portion 5001 mounted in the housing 5000 serving as a bezelincludes a non-rectangular display region. The display portion 5001 candisplay an icon 5020 indicating time, another icon 5021, and the like.

The electronic devices illustrated in FIGS. 18A to 18H can have avariety of functions, for example, a function of displaying a variety ofinformation (e.g., a still image, a moving image, and a text image) on adisplay portion, a touch panel function, a function of displaying acalendar, date, time, and the like, a function of controlling processingwith a variety of software (programs), a wireless communicationfunction, a function of being connected to a variety of computernetworks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, and a function of reading a program or datastored in a recording medium and displaying the program or data on adisplay portion. Furthermore, the electronic device including aplurality of display portions can have a function of displaying imageinformation mainly on one display portion while displaying textinformation mainly on another display portion, a function of displayinga three-dimensional image by displaying images where parallax isconsidered on a plurality of display portions, or the like. Furthermore,the electronic device including an imaging portion can have a functionof photographing a still image, a function of photographing a movingimage, a function of automatically or manually correcting a photographedimage, a function of storing a photographed image in a recording medium(an external recording medium or a recording medium incorporated in acamera), a function of displaying a photographed image on the displayportion, or the like. Note that functions that can be provided for theelectronic devices illustrated in FIGS. 18A to 18H are not limited tothe above, and the electronic devices can have a variety of functions.

The electronic devices described in this embodiment are characterized byincluding a display portion for displaying some sort of information. Thedisplay device described in the above embodiment can be employed for thedisplay portion.

At least part of this embodiment can be implemented in combination withany of the other embodiments described in this specification asappropriate.

This application is based on Japanese Patent Application serial no.2015-053631 filed with Japan Patent Office on Mar. 17, 2015, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A touch panel comprising: a substrate; a thirdconductive layer over the substrate; a fourth conductive layer apartfrom the third conductive layer on a same plane; a liquid crystal layerover the third conductive layer and the fourth conductive layer; asecond conductive layer over the liquid crystal layer; a firstconductive layer over the second conductive layer; and a sixthconductive layer apart from the first conductive layer on a same plane;wherein the first conductive layer has a mesh shape comprising aplurality of openings, wherein the sixth conductive layer has a meshshape comprising a plurality of openings, wherein the second conductivelayer has a portion overlapping with the first conductive layer, aportion overlapping with the third conductive layer, and a portionoverlapping with the fourth conductive layer, wherein the thirdconductive layer comprises a portion overlapping with one of theplurality of openings of the first conductive layer, wherein the fourthconductive layer comprises a portion overlapping with a regionsurrounded by the first conductive layer and the sixth conductive layer,and wherein part of the first conductive layer is between the thirdconductive layer and the fourth conductive layer in a plan view.
 2. Thetouch panel according to claim 1, wherein the second conductive layerfunctions as a common electrode, and wherein the third conductive layerand the fourth conductive layer each function as a pixel electrode. 3.The touch panel according to claim 1, wherein the second conductivelayer is electrically connected to a terminal supplied with a constantpotential.
 4. The touch panel according to claim 1, wherein a spacer isover the third conductive layer and below the second conductive layer,and wherein the spacer comprises a portion overlapping with the firstconductive layer.
 5. A touch panel comprising: a substrate; a thirdconductive layer over the substrate; a fourth conductive layer apartfrom the third conductive layer on a same plane; a liquid crystal layerover the third conductive layer and the fourth conductive layer; asecond conductive layer over the liquid crystal layer; a firstconductive layer over the second conductive layer; and a sixthconductive layer apart from the first conductive layer on a same plane;wherein the first conductive layer is configured to block visible lightand has a mesh shape comprising a plurality of openings, wherein thesixth conductive layer is configured to block visible light and has amesh shape comprising a plurality of openings, wherein the secondconductive layer is configured to transmit visible light and has aportion overlapping with the first conductive layer, a portionoverlapping with the third conductive layer, and a portion overlappingwith the fourth conductive layer, wherein the third conductive layer andthe fourth conductive layer are each configured to reflect visiblelight, wherein the third conductive layer comprises a portionoverlapping with one of the plurality of openings of the firstconductive layer, wherein the fourth conductive layer comprises aportion overlapping with a region surrounded by the first conductivelayer and the sixth conductive layer, and wherein part of the firstconductive layer is between the third conductive layer and the fourthconductive layer in a plan view.
 6. The touch panel according to claim5, wherein the second conductive layer functions as a common electrode,and wherein the third conductive layer and the fourth conductive layereach function as a pixel electrode.
 7. The touch panel according toclaim 5, wherein the second conductive layer is electrically connectedto a terminal supplied with a constant potential.
 8. The touch panelaccording to claim 5, wherein a spacer is over the third conductivelayer and below the second conductive layer, and wherein the spacercomprises a portion overlapping with the first conductive layer.